Damping systems of this kind, also called “pendulum oscillator” or “pendulum” devices and installed especially but not exclusively on the transmission of a motor vehicle, are known from the existing art.
In a motor vehicle transmission, at least one torsional damping system is generally combined with a clutch able to selectively connect the engine to the gearbox, such as a friction clutch or a hydrokinetic coupling apparatus having a locking clutch, the purpose being to filter vibrations resulting from engine irregularities.
This is because a combustion engine exhibits irregularities due to the successive combustion events in the engine's cylinders, said irregularities varying in particular depending on the number of cylinders.
The damping means of a torsional damping system consequently have the function of filtering the vibrations caused by the irregularities, and take effect before engine torque is transmitted to the gearbox.
Vibrations entering the gearbox would otherwise cause shocks, noise, or acoustic impacts therein that are particularly undesirable.
This is one of the reasons why one or more damping means, able to filter vibrations at least at one defined frequency, are used.
In the sector of transmissions, the search for increasingly high filtering performance has led to the addition, for certain applications, of a damping system of the pendulum oscillator type to the damping systems or dampers that are conventionally utilized both in friction clutches and in hydrokinetic coupling devices of motor vehicles.
The document US 2010/0122605 represents one such damping system of the pendulum oscillator type.
The damping system has a support member and at least one pair of flyweights, generally several pairs of flyweights, distributed circumferentially over the periphery of the support member.
The pairs of flyweights are arranged around the rotation axis of the engine shaft, and each pair of flyweights is free to oscillate around an imaginary axis substantially parallel to the rotation axis of the engine shaft.
As illustrated in FIG. 4 of this document, the flyweights of one pair are connected to one another by connecting means such as rivets, each connecting means passing through an opening configured for that purpose in the support member, and the ends of the connecting means each being integral with one of the flyweights of the pair, for example fastened to the flyweights by riveting.
Besides the connecting means, the damping means has at least one device for guiding the flyweights with respect to the support member, the guidance device having bearing elements such as cylindrical rollers.
Each bearing element interacts with a pair of opposite tracks, respectively a first track carried by each of the flyweights of the pair and a second track formed by one of the edges of an orifice that encompasses the support member.
In reaction to rotational inconsistencies, said flyweights become displaced in such a way that the center of gravity of each of the flyweights oscillates around an axis substantially parallel to the rotation axis of the engine shaft.
The radial position of the center of gravity of each of the flyweights with respect to the rotation axis of the engine shaft, as well as the distance of said center of gravity with respect to the imaginary oscillation axis, are established so that in response to centrifugal forces, the oscillation frequency of each of the flyweights is proportional to the rotation speed of the engine shaft; said multiple can assume, for example, a value close to the predominant harmonic order of the vibrations responsible for strong rotational inconsistencies at close to idle speed.
As illustrated in FIG. 4 of the document US 2010/0122605, the damping system has three rivets and two bearing elements that are interposed circumferentially between two consecutive rivets.
A damping system of this kind, however, and very particularly the device for guiding the flyweights, is not entirely satisfactory and exhibits a variety of drawbacks.
The support member is weakened by the presence on the one hand of openings to allow passage of the connecting means, and on the other hand of guidance orifices associated with the bearing elements.
In the example of the document US 2010/0122605, for each pair of flyweights there are thus no fewer than five cutouts required, respectively three openings and two orifices, said cutouts affecting the mechanical strength of the support member.
In addition, the presence of cutouts likewise has an effect on the design of the damping system, given that the openings and orifices, arranged circumferentially on the radial periphery of the support member and successively one alongside the others, limit the number of flyweight pairs that can be installed on a support member of a given diameter.
A damping system of this kind, of the two-strand pendulum type, requires very good cutout stamping quality, which is difficult to achieve given the stamping processes used in industrial production.
This is because usual stamping processes result in the presence of scratches or ridges in the axial direction, i.e. along the thickness.
In the case of the support member, for example, such scratches are present on the edge of each orifice forming the second guidance track with which the bearing element interacts, since the two orifices in the support member, and very particularly of each of the second guidance tracks, are generally produced by conventional press-type stamping.
These surface finish problems also occur with the flyweights having the first guidance tracks for the bearing elements, which are produced on a press by stamping out the flyweights, followed by a trimming operation.
The surface finish of the guidance tracks determines the bearing quality, however, especially the smoothness of motion during rolling. In addition, the surface finish of the guidance tracks has an effect on wear on the bearing element, and on the maximum sustainable contact pressure.
Other specific stamping processes could be utilized in order to improve the surface finish of the guidance tracks, but would then have unacceptable consequence in terms of cost.
In addition, the implementation of at least one orifice order to form, in each of the flyweights, the second guidance track associated with said at least one bearing element results in a commensurate reduction in the total mass of each flyweight, and consequently in the operating efficiency of the damping system, which has a lower total mass for a given overall size.
The axial length of the bearing elements, such as the rollers, also implies a risk of skewing of the flyweights with respect to the support member.
Lastly, when the damping system is under centrifugal force, the bearing elements are then operating in flexural mode, inducing large mechanical stresses in the elements as well as wear problems.
The object of the present invention is therefore very particularly to propose a design that allows the aforementioned drawbacks of a damping system of this kind to be overcome and allows its performance to be improved, while in particular retaining a small overall size and optimum functioning.